> (and the US
> military seem to drop the colon as in "1800" and say strange things like
> "eighteen hundred hours" instead of "eighteen o'clock").

They say "klicks" for "kilometers", too.

> I really wonder, why the modern notation doesn't
> catch on in the US, where even air travel tickets still use the awkward
> notation (and solve the ambiguity problem by never scheduling any event
> exactly on noon or midnight).

You underestimate the tendency of Americans to think that the way they
do it is the way God intended (*and* to consider that of paramount
importance).